Using somatic cell hybrids between rodent and human cells we have assigned the genes for alpha and beta subunits of hexosaminidase A to human chromosomes 15 and 5 respectively, the gene for beta glucuronidase to human chromosome 7, the genes for mannosephosphate isomerase and phosphoglicerate kinase to the distal half of human chromosome 15 and the gene for cytoplasmic glutamic oxaloacetic transaminase to the distal third of the long arm of chromosome 10. At present we are studying hybrids between rodent and human cells carrying translocations involving human chromosome 1, 7, 9, 15 and 17 to determine the regional location of genes assigned to these chromosomes. In addition we are investigating hybrids between transformed human cells and normal human cells derived from patients with beta glucuronidase deficiency for the production of heteropolymers between the normal and the mutant enzyme. BIBLIOGRAPHIC REFERENCES: Orkwiszewski, K.G., T.A. Tedesco, W.J. Mellman, and C.M. Croce. Linkage relationship between the genes for thymidine kinase and galactokinase in different primates. Somatic Cell Genetics, 2:21-26, 1976. Strand, M., J.T. August, and C.M. Croce. Selective induction of murine oncornavirus gene expression in somatic cell hybrids between mouse peritoneal macrophages and SV40-transformed human cells. Virology, 70:545-549, 1976.